As a key technology in NGN, the label switching technology plays a more and more important role in IP networks. The label switching technology was initially put forward to raise the forwarding speed of routers, but is now widely used in traffic engineering, Virtual Private Network (VPN), Quality of Service (QoS), etc. owing to its own advantage, and increasingly becomes an important standard for large-scale IP networks.
In a label switching network, data packets are forwarded through label switching, and the forwarding path of the data packets in the label switching network is called label switching path (LSP), which is defined by swapping label values. The label values of the data packets are switched in each label switching router (LSR), which includes an Ingress LSR and an Egress LSR. As the label switching technology is becoming a key technique for the multi-service bearer in the IP networks, an efficient use of the limited bandwidth resources of the label switching network to realize data forwarding with protection has become the focus of concern in the telecommunication industry.
To realize the data forwarding with protection, the International Telecommunications Union(ITU) Y.1720 standard specifies two data forwarding methods on the existing packet switching networks including the label switching network: the 1:1 (One to One) mode and the 1+1 (One plus One) mode. Descriptions are hereinafter given, respectively, to the implementing principles of the two methods for the data forwarding in the label switching networks.
In the 1:1 mode two LSPs are provided for the same data flow for forwarding, which include a main LSP and a standby LSP. The main LSP is used in the normal state, and the standby LSP is, in a sense, a protection for the main LSP, which means that when the main LSP is working normally, the standby LSP is idle, and when the main LSP has a failure, the data flow would be switched to the standby LSP by the source end, i.e. the ingress LSR.
In the 1+1 mode, the same data flow is distributed to two LSPs at the source end, through which the flow is forwarded at the same time, and then the destination end, i.e. the egress LSR, selects one from the main and standby LSPs to receive the data flow.